Well, simple to test, take the Crate_A FBX that is in the new angry bots demo, add it to your assets folder in a new empty project, change the import scale from 0.01 to 1.0, drag it into your scene, add a plane, scale at 100,1,100, add a mesh collider to the plane, maybe a texture or color to make it stand out.
Next take that crate that you dragged into the scene and add a mesh collider to it, apply it back to the prefab and also add a rigid body to the crate, this way it can fall from the sky. Once applied back to the prefab, remove the crate from the scene and then write code to instantiate a clone of that prefab into the scene at above the plane by 8 meters (0,8,0), the crate will fall and go through the plane. Add a sphere to the scene at 1 meter in diameter, have a sphere collider on it, and rigid body, 2 meters above the plane so that it falls onto the plane, the crate above the sphere at the 8 meters, the sphere will collide with the plane, the crate will collide with the sphere, fall off and through the plane…
Next, change the collider on the crate from mesh collider to box collider, it will then fall to the sphere, collide and bound off the sphere and collide with the plane.
I have been able to reproduce this on 2 machines so far, would open a ticket however my ticket queue is so full that I never get a response from the ticket system, haven’t for like a year now so if someone can repeat and verify this, please open a ticket.
Enjoy, was a cute experiment, unfortunately I have found that mesh colliders use less power to do than box colliders for some strange reason. I can have over 100 mesh collision objects in a given scene going on with stuff with no chop but when I start with over 100 box colliders, I get hiccups which is repeatable on builds for my iMac, MacBook Pro, PC (both desktop and laptop) along with Andriod / iPad / iPad 2 and iPhone / iPod touch. I want to stick with mesh colliders!